Fungus blight Ascochyta attacks more pulse crops

Jan. 31, 2012

Ascochyta pod infection. Signficant amounts of pulse crops are being found to contain fungus blight Ascochyta.

BOZEMAN — Researchers at Montana State University are seeing an increase in the number of samples of pulse crops containing significant amounts of the fungus blight Ascochyta over the past year.

The findings represent an increase compared to researchers found in the 2010 samples, particularly in the lentil crop. With pulse crops going into the ground soon, there is some confusion about the acceptable level of Ascochyta in a given crop.

Ascochyta is a potentially serious fungal disease in pulse crops, including lentils, peas and chickpea. The disease can defoliate plants and spread rapidly. One way to prevent Ascochyta blight is to plant fungus-free seed. Growers can test seed lots for Ascochyta, by sending a sample to the MSU Seed Lab.

The test takes 10 days after the seed is plated, as the fungus needs to grow out of the seeds before it can be identified. Send seed to the MSU Seed Lab now to leave plenty of time to receive the results and make management decisions before planting.

While there are no definitive acceptable levels of the fungus, there are guidelines:

There is a 0 percent tolerance for chickpea because it is very susceptible to Ascochyta blight.

Pea and lentil are more resistant, so MSU plant pathologist Mary Burrows recommends less than 2 percent to 5 percent Ascochyta in the seed for these crops.

There are no definitive thresholds for disease development. A higher number may indicate a greater risk for disease development because more fungus goes into the field, but it does not necessarily mean the disease will manifest. Conversely, a low/zero number does not mean the disease will not occur. The disease requires a susceptible crop, the pathogen and a conducive environment.

If the level of Ascochyta is above the threshold, Burrows recommends using LSP/Mertect fungicide at planting. This is the only seed-treatment fungicide with good efficacy against Ascochyta blight according to MSU trials. This is applied in addition to seed treatment to control damping off and root rots.

Dynasty (azoxystrobin) also can be effective for lentils, but is not registered for peas and not recommended for chickpea because it's a strobilurin.

The species of Ascochyta causing blight in chickpea in Montana and North Dakota is resistant to strobilurin fungicides. There are a number of fungicide options if disease develops in the field, but application soon after disease onset is critical for the control of this rapidly spreading disease.

For specific directions, call the Seed Lab at 406-994-2141 or visit online at plant sciences.montana.edu /seedlab.